Topic: Anyone Have Part Numbers for These? (750 F1 Pistons)

[MacM2010]

Hi all:

So, my 1976 750F1 has decided to destroy me.  Well, my bank account, at least, and perhaps my sanity.  (Could be worse, I could have invested my money in the stock market.)

Porscheguy912 and I are rebuilding the engine, and one of the pistons is no more.  Long story.  Anyway, we bought a new piston to replace it, but (as an earlier post shows), it doesn't match the other three.  Now, all the fiches I've seen have two options for pistons for the 76 F, or, in other words, two part numbers available for stock pistons.  They are:

13101-392-020
and
13101-392-000

Now, the pictures I have below are of two pistons.  One (the shiny one) comes from a guy on eBay who sold us a NOS piston (don't worry, it was cheap) with a part number (on the box) of 13101-392-020.  The other, dirtier one with the pin in it comes out of the bike, and we have no part number for it.

What I'm hoping is that the piston from the bike is the part with the # ending in 000.  But it's also possible that the NOS piston is in the wrong box, or that the pistons in the bike are from a different engine, or I've simply lost my mind. 

Please, someone, tell me the part # for the dirty piston with the pin.  It's slightly domed on top and has "E 392" on the side (which my impressive detective skills tell me is part of the part #).  The NOS piston has a raised section on top, and has "S 392" on the side, as well as what appears to be the number 6.  I don't want to buy the "000" stock piston without being sure it's the right one, so if anyone can assist with a little knowledge (that I sorely lack), I'll be very grateful.

Thanks for looking,
Mac

[MacM2010]

Another pic:

[MacM2010]

And here's the tops.  I have a few more pics, if they'll help, but they seem redundant to me.  The pistons do say "Honda" on them, so at least I think they're meant for this engine. 

[Clyde]

I cannot help with the numbers as I have only seen the raised section pistons.
But if the weight of the piston and the compression ratio are the same then why not use the new piston.
Not ideal maybe, but I cannot see why not
Also are the ring grooves the same?

[mcpuffett]

If its any help i have the same domed top pistons in my 78 registered F1 here in the uk & i have seen the flat top ones in a k7 motor, cheers Mick.

[mcpuffett]

Hi I just did a bit of searching for you on CMSNL site and it appears that both of those parts numbers are for the F1, 13101 392 000 is the part number you are looking for to replace your damaged piston, my F1 which is a couple of years younger than yours has the other type of pistons fitted,  cheers Mick.

[MacM2010]

Ah-ha!  So it is the 000 part?  That's very good news, thanks mcpuffett.  I thought I was going to have to buy a Harley.   

I was considering ordering the part through an out-of-town dealer.  That way if it showed up and was the wrong piece, I could just take off and never go back.  But this way seems easier and slightly more ethical.

Thanks guys!
Mac

[Jerry Rxman Griffin aka MuthaF'er]

Mac,

What's the serial number on your engine? I'll check when I get back home tomorrow. If you can't get a new piston there are lots of used ones around. I too have one of those sets of 3 but I tend to hang on to everything.

Jerry

[MacM2010]

Engine number CB750E-2540180.  We checked and the case is definitely an F1 engine, and 392 is the correct F piston number (the problem is that both pistons have it).  A kind forum member was nice enough to send us a piston from a busted K engine, but it sadly doesn't match. 

From this and my other "piston" post, I'm fairly sure it's the 000 piston that I need.  I can get one, I just want to be sure it's right before I buy it.

Thanks again!
Mac

[MacM2010]

I think I just answered my own question.  First time for everything, I guess...

From eBay, in Spain:

[mcpuffett]

Hi Mac, glad to help you and you found a piston to  , cheers Mick.

[MacM2010]

Thanks very much, guys.  You really do meet the nicest people on a Honda.

Now, let's see if we can get her running...

[Jerry Rxman Griffin aka MuthaF'er]

Honda switched to the -020 piston at engine serial number 2551568.

I took my K8 -392 engine apart to find -020 pistons which are also labeled -392

Lesson here is to ALSO go by engine numbers. Glad you solved your problem.